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What is the softest crystal?
I guess the honor for the softest crystal will have to go to the mineral talc, which has a hardness of one (1) on the Mohs Hardness Scale. Talc is a silicate (like many of the earth's most important minerals), and contains magnesium and a bit of water along with the silica and oxygen. Talc is usually associated with metamorphic rocks, and while it is pretty common in nature it is actually rather rare in crystal form. It belongs to the monoclinic crystal system, but is most commonly found in granular or fibrous masses. Because of its softness and perfect cleavage in one (1) direction (like the graphite in pencils), it makes a great lubricant in situations where it won't be put under too much stress (like the "talcum powder" which is commonly found lubricating and protecting the posterior portions of babies). Some impure varieties of talc are called "soapstone" because of their slippery, greasy feel. When found in massive, compact chunks, soapstone can be carved like marble (although due to its softness it is rather fragile).
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